A swing control apparatus for a construction machine in the related art as illustrated in FIG. 1 includes a swing operation lever 1, a hydraulic pump 2 connected to an engine, a hydraulic swing motor 3 that makes an upper swing structure swing when the hydraulic swing motor is driven by hydraulic fluid supplied from a hydraulic pump (not illustrated), a swing parking brake 4 that is released in accordance with an input of an operation signal of the swing operation lever 1, and a control valve 6 which drives a hydraulic cylinder 5 for the swing parking brake by the hydraulic fluid from the hydraulic pump 2 to release the swing parking brake 4 if the control valve 6 is shifted by an input of the operation signal from the swing operation lever 1.
In the hydraulic swing control apparatus as described above, if the swing operation lever 1 is operated by an operator, an operation signal is supplied to an opposite side of a valve spring 6a of the control valve 6 to shift a spool in a downward direction in the drawing. Due to this, hydraulic fluid that is discharged from the hydraulic pump 2 is supplied to the hydraulic cylinder 5 for the swing parking brake through the shifted control valve 6 to press a spring 7. At this time, since the swing parking brake 4 that holds a swing motor shaft 8 is shifted to a release state, the swing motor 3 is driven by the hydraulic fluid from the hydraulic pump to make an upper swing structure to swing against a lower driving structure.
If an error occurs in the hydraulic swing motor 3 that makes the upper swing structure swing, a problem occurs to cause appearance of an abnormal phenomenon in the equipment. At this time, the operator can directly recognize the occurrence of the problem, and thus can take emergency measures accordingly.
On the other hand, a construction machine, such as a hybrid excavator on which a swing apparatus that makes the upper swing structure swing against the lower driving structure using an electric swing motor that is driven by electric energy is mounted, has been used.
A swing control apparatus for a hybrid construction machine in the related art is provided with a press button type emergency button which is installed in a position that the operator can easily reach during working so that the operator can recognize and immediately cope with an emergency situation where an error occurs in the electric swing device during the swing operation of the upper swing structure. Further, if the emergency situation occurs during working, the operator may pull down a safety lever to intercept main power supply to the swing motor side.
As described above, if the emergency situation occurs during working, the operator can immediately take emergency measures based on the operator's judgment.
On the other hand, in the swing control apparatus for a hybrid construction machine, the driving direction and the driving speed of the swing motor are controlled in accordance with a control signal that is transmitted from a controller (V-ECU) of the equipment. Due to this, even in the emergency situation where an electric trouble occurs in a power system such as a power conversion device for controlling the swing motor, the operator is unable to directly recognize the occurrence of the emergency situation.
Accordingly, even in the case where an emergency situation occurs in the swing device during working on a slope, the operator is unable to immediately take emergency measures, and this may cause the occurrence of secondary accidents, such as a turnover of the equipment or injury of the operator.